Golf ball

ABSTRACT

A golf ball  2  has a large number of dimples  10  on a surface thereof. The golf ball  2  meets the following mathematical formula (I): 
         Y ≦3.8* X −2.894   (I),
 
     where X represents a ratio of a sum of areas of all the dimples  10  to a surface area of a phantom sphere of the golf ball, and Y represents a standard deviation (mm) of diameters of all the dimples  10.

This application claims priority on Patent Application No. 2012-017172 filed in JAPAN on Jan. 30, 2012. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to golf balls. Specifically, the present invention relates to improvement of dimples of golf balls.

2. Description of the Related Art

Golf balls have a large number of dimples on the surfaces thereof. The dimples disturb the air flow around the golf ball during flight to cause turbulent flow separation. This phenomenon is referred to as “turbulization”. Due to the turbulization, separation points of the air from the golf ball shift backwards leading to a reduction of drag. The turbulization promotes the displacement between the separation point on the upper side and the separation point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. Excellent dimples efficiently disturb the air flow. The excellent dimples produce a long flight distance.

There have been various proposals for dimples. JP2005-137692 (US2005/0101412) discloses a golf ball in which the standard deviation of the diameters of dimples are equal to or less than 0.52. JP2007-175267 (US2007/0149321) discloses a golf ball in which the number of units in a dimple pattern near each pole is different from the number of units in a dimple pattern near the equator. JP2007-195591 (US2007/0173354) discloses a golf ball in which the ratio of the number of dimples having diameters of 3.40 mm or greater to the total dimple number is equal to or greater than 90%. JP2008-389 (US2007/0298908) discloses a golf ball in which the pitch between adjacent dimples is small.

JP2009-95593 (US2009/0102097) discloses a golf ball that has dimples located on the equator. Similar golf balls are disclosed also in JP2009-95589 (the aforementioned US2009/0102097), JP2010-57612 (US2010/0052219), and JP2010-57623 (the aforementioned US2010/0052219).

The ratio of the sum of the areas of all dimples to the surface area of a phantom sphere of the golf ball is referred to as an occupation ratio. The occupation ratio influences the flight performance of the golf ball. It is known to one skilled in the art that a golf ball having a high occupation ratio has excellent flight performance.

The standard deviation of the diameters of dimples influences the flight performance of the golf ball. It is known to one skilled in the art that a golf ball in which the standard deviation is low has excellent flight performance.

When small dimples are arranged in narrow zones each surrounded by a plurality of dimples, a dimple pattern that provides a high occupation ratio is obtained. However, the small dimples are unlikely to contribute to turbulization. In a golf ball having such small dimples, the standard deviation is high. The occupation ratio and the standard deviation are contradictory to each other.

The greatest interest to golf players concerning golf balls is flight distance. In light of flight performance, there is room for further improvement in a dimple pattern. An object of the present invention is to provide a golf ball having excellent flight performance.

SUMMARY OF THE INVENTION

A golf ball according to the present invention has a large number of dimples on a surface thereof. The golf ball meeting the following mathematical formula (I):

Y≦3.8*X−2.894   (I),

where X represents a ratio of a sum of areas of all the dimples to a surface area of a phantom sphere of the golf ball, and Y represents a standard deviation (mm) of diameters of all the dimples.

In the golf ball according to the present invention, turbulization is prompted. The golf ball has excellent flight performance.

Preferably, the ratio X is equal to or greater than 0.78. Preferably, the ratio X is equal to or less than 0.95. Preferably, the standard deviation Y is equal to or less than 0.30 mm.

Preferably, a number of the dimples is equal to or greater than 300 but equal to or less than 400. Preferably, a contour of each dimple is circular.

Preferably, a diameter of each dimple is equal to or greater than 2.0 mm but equal to or less than 6.0 mm. Preferably, a depth of each dimple is equal to or greater than 0.05 mm but equal to or less than 0.60 mm. Preferably, a total volume of the dimples is equal to or greater than 250 mm³ but equal to or less than 400 mm³.

Preferably, the golf ball meets the following mathematical formula (II):

Y≦3.8*X−2.944   (II).

Preferably, the golf ball meets the following mathematical formula (III):

Y≦3.8*X−2.994   (III).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball according to one embodiment of the present invention;

FIG. 2 is an enlarged plan view of the golf ball in FIG. 1;

FIG. 3 is a bottom view of the golf ball in FIG. 2;

FIG. 4 is a right side view of the golf ball in FIG. 2;

FIG. 5 is a front view of the golf ball in FIG. 2;

FIG. 6 is a left side view of the golf ball in FIG. 2;

FIG. 7 is a back view of the golf ball in FIG. 2;

FIG. 8 is a graph showing the relationship between an occupation ratio X and a standard deviation Y;

FIG. 9 is a partially enlarged cross-sectional view of the golf ball in FIG. 1;

FIG. 10 is a plan view of a golf ball according to Example 1 of the present invention;

FIG. 11 is a bottom view of the golf ball in FIG. 10;

FIG. 12 is a right side view of the golf ball in FIG. 10;

FIG. 13 is a front view of the golf ball in FIG. 10;

FIG. 14 is a left side view of the golf ball in FIG. 10;

FIG. 15 is a back view of the golf ball in FIG. 10;

FIG. 16 is a plan view of a golf ball according to Example 3 of the present invention;

FIG. 17 is a bottom view of the golf ball in FIG. 16;

FIG. 18 is a right side view of the golf ball in FIG. 16;

FIG. 19 is a front view of the golf ball in FIG. 16;

FIG. 20 is a left side view of the golf ball in FIG. 16;

FIG. 21 is a back view of the golf ball in FIG. 16;

FIG. 22 is a plan view of a golf ball according to Example 4 of the present invention;

FIG. 23 is a bottom view of the golf ball in FIG. 22;

FIG. 24 is a right side view of the golf ball in FIG. 22;

FIG. 25 is a front view of the golf ball in FIG. 22;

FIG. 26 is a left side view of the golf ball in FIG. 22;

FIG. 27 is a back view of the golf ball in FIG. 22;

FIG. 28 is a plan view of a golf ball according to Example 5 of the present invention;

FIG. 29 is a bottom view of the golf ball in FIG. 28;

FIG. 30 is a right side view of the golf ball in FIG. 28;

FIG. 31 is a front view of the golf ball in FIG. 28;

FIG. 32 is a left side view of the golf ball in FIG. 28;

FIG. 33 is a back view of the golf ball in FIG. 28;

FIG. 34 is a plan view of a golf ball according to Example 6 of the present invention;

FIG. 35 is a bottom view of the golf ball in FIG. 34;

FIG. 36 is a right side view of the golf ball in FIG. 34;

FIG. 37 is a front view of the golf ball in FIG. 34;

FIG. 38 is a left side view of the golf ball in FIG. 34;

FIG. 39 is a back view of the golf ball in FIG. 34;

FIG. 40 is a plan view of a golf ball according to Example 7 of the present invention;

FIG. 41 is a bottom view of the golf ball in FIG. 40;

FIG. 42 is a right side view of the golf ball in FIG. 40;

FIG. 43 is a front view of the golf ball in FIG. 40;

FIG. 44 is a left side view of the golf ball in FIG. 40; and

FIG. 45 is a back view of the golf ball in FIG. 40.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention, based on preferred embodiments with reference to the accompanying drawings.

A golf ball 2 shown in FIG. 1 includes a spherical core 4, a mid layer 6 positioned outside the core 4, and a cover 8 positioned outside the mid layer 6. On the surface of the cover 8, a large number of dimples 10 are formed. Of the surface of the golf ball 2, a part other than the dimples 10 is a land 12. The golf ball 2 includes a paint layer and a mark layer on the external side of the cover 8 although these layers are not shown in the drawing.

The golf ball 2 has a diameter of preferably 40 mm or greater but 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm. The golf ball 2 has a weight of preferably 40 g or greater but 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is particularly preferably equal to or less than 45.93 g.

The core 4 is formed by crosslinking a rubber composition. Examples of the base rubber of the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and high-cis polybutadienes are particularly preferred.

In order to crosslink the core 4, a co-crosslinking agent is suitably used. Examples of preferable co-crosslinking agents in light of resilience performance include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. The rubber composition preferably includes an organic peroxide together with a co-crosslinking agent. Examples of preferable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.

According to need, various additives such as a filler, sulfur, a vulcanization accelerator, a sulfur compound, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like are included in the rubber composition of the core 4 in an adequate amount. Synthetic resin powder or crosslinked rubber powder may also be included in the rubber composition.

The core 4 has a diameter of preferably 30.0 mm or greater and particularly preferably 38.0 mm or greater. The diameter of core 4 is preferably equal to or less than 42.0 mm and particularly preferably equal to or less than 41.5 mm. The core 4 may be composed of two or more layers. The core 4 may have a rib on the surface thereof. The core 4 may be hollow.

A suitable polymer for the mid layer 6 is an ionomer resin. Examples of preferable ionomer resins include binary copolymers formed with an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of other preferable ionomer resins include ternary copolymers formed with: an α-olefin; an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. For the binary copolymer and the ternary copolymer, preferable α-olefins are ethylene and propylene, while preferable α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In the binary copolymer and the ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of metal ions for use in neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion, and neodymium ion.

Instead of an ionomer resin, other polymers may be used for the mid layer 6. Examples of the other polymers include polystyrenes, polyamides, polyesters, polyolefins, and polyurethanes. Two or more polymers may be used in combination.

According to need, a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the mid layer 6 in an adequate amount. For the purpose of adjusting specific gravity, powder of a metal with a high specific gravity such as tungsten, molybdenum, and the like may be included in the mid layer 6.

The mid layer 6 has a thickness of preferably 0.2 mm or greater and particularly preferably 0.3 mm or greater. The thickness of the mid layer 6 is preferably equal to or less than 2.5 mm and particularly preferably equal to or less than 2.2 mm. The mid layer 6 has a specific gravity of preferably 0.90 or greater and particularly preferably 0.95 or greater. The specific gravity of the mid layer 6 is preferably equal to or less than 1.10 and particularly preferably equal to or less than 1.05. The mid layer 6 may be composed of two or more layers.

The cover 8 is formed from a resin composition. The base polymer of the resin composition is a polyurethane. Thermoplastic polyurethanes and thermosetting polyurethanes can be used. In light of productivity, thermoplastic polyurethanes are preferred. A thermoplastic polyurethane includes a polyurethane component as a hard segment, and a polyester component or a polyether component as a soft segment.

Examples of a curing agent for the polyurethane component include alicyclic diisocyanates, aromatic diisocyanates, and aliphatic diisocyanates. Alicyclic diisocyanates are particularly preferred. Since an alicyclic diisocyanate does not have any double bond in the main chain, the alicyclic diisocyanate suppresses yellowing of the cover 8. Examples of alicyclic diisocyanates include 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), 1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI), isophorone diisocyanate (IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI). In light of versatility and processability, H₁₂MDI is preferred.

Instead of a polyurethane, other polymers may be used for the cover 8. Examples of the other polymers include ionomer resins, polystyrenes, polyamides, polyesters, and polyolefins. Two or more polymers may be used in combination.

According to need, a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the cover 8 in an adequate amount.

The cover 8 has a thickness of preferably 0.2 mm or greater and particularly preferably 0.3 mm or greater. The thickness of the cover 8 is preferably equal to or less than 2.5 mm and particularly preferably equal to or less than 2.2 mm. The cover 8 has a specific gravity of preferably 0.90 or greater and particularly preferably 0.95 or greater. The specific gravity of the cover 8 is preferably equal to or less than 1.10 and particularly preferably equal to or less than 1.05. The cover 8 may be composed of two or more layers.

The golf ball 2 may include a reinforcing layer between the mid layer 6 and the cover 8. The reinforcing layer firmly adheres to the mid layer 6 and also to the cover 8. The reinforcing layer suppresses separation of the cover 8 from the mid layer 6. Examples of the base polymer of the reinforcing layer include two-component curing type epoxy resins and two-component curing type urethane resins.

As shown in FIGS. 2 to 7, the contour of each dimple 10 is circular. The dimples 10 whose contours are circular have excellent aerodynamic symmetry. The golf ball 2 has dimples A each having a diameter of 4.50 mm; dimples B each having a diameter of 4.40 mm; dimples C each having a diameter of 4.30 mm; and dimples D each having a diameter of 4.15 mm. The number of types of the dimples 10 is four.

The number of the dimples A is 28; the number of the dimples B is 122; the number of the dimples C is 100; and the number of the dimples D is 74. The total number N of the dimples 10 is 324. The average of the diameters of all the dimples 10 is 4.321 mm.

The area s of the dimple 10 is the area of a region surrounded by the contour line when the center of the golf ball 2 is viewed at infinity. In the case of a circular dimple 10, the area s is calculated by the following mathematical formula.

s=(Dm/2)²*π

In this mathematical formula, Dm represents the diameter of the dimple 10. In the golf ball 2 shown in FIGS. 2 to 7, the area of each dimple A is 15.90 mm²; the area of each dimple B is 15.21 mm²; the area of each dimple C is 14.52 mm²; and the area of each dimple D is 13.53 mm².

The ratio of the sum of the areas s of all the dimples 10 to the surface area of a phantom sphere is referred to as an occupation ratio X. In light of turbulization, the occupation ratio X is preferably equal to or greater than 0.78, more preferably equal to or greater than 0.79, and particularly preferably equal to or greater than 0.80. The occupation ratio X is preferably equal to or less than 0.95. In the golf ball 2 shown in FIGS. 2 to 7, the total area of all the dimples 10 is 4753.5 mm². The surface area of the phantom sphere of the golf ball 2 is 5728.0 mm², and thus the occupation ratio X is 0.830.

The standard deviation Y of the diameters of all the dimples 10 is preferably equal to or less than 0.30. In the golf ball 2 in which the standard deviation Y is equal to or less than 0.30, turbulization is prompted. In this respect, the standard deviation Y is more preferably equal to or less than 0.29 and particularly preferably equal to or less than 0.28. The standard deviation Y may be zero. The standard deviation Y of the golf ball 2 shown in FIGS. 2 to 7 is calculated by the following mathematical formula.

Y=(((4.500−4.321)²*28+(4.400−321)²*22+(4.300−321)²*100+(4.150−4.321)²*74)/324)^(1/2)

The standard deviation Y of the golf ball 2 is 0.109.

In the graph of FIG. 8, the horizontal axis indicates an occupation ratio, and the vertical axis indicates a standard deviation Y. A straight line indicated by a reference sign L1 in the graph of FIG. 8 is represented by the following mathematical formula.

Y=3.8*X−2.894

According to the finding by the inventor of the present invention, the golf ball 2 whose coordinate (X,Y) is on or below the straight line L1 has excellent flight performance. In other words, the golf ball 2 that meets the following mathematical formula (I) has excellent flight performance. The reason is inferred to be that turbulization is prompted.

Y≦3.8*X−2.894   (I)

A straight line indicated by a reference sign L2 in the graph of FIG. 8 is represented by the following mathematical formula.

Y=3.8*X−2.944

According to the finding by the inventor of the present invention, the golf ball 2 whose coordinate (X,Y) is on or below the straight line L2 has further excellent flight performance. In other words, the golf ball 2 that meets the following mathematical formula (II) has excellent flight performance. The reason is inferred to be that turbulization is prompted.

Y≦3.8*X−2.944   (II)

A straight line indicated by a reference sign L3 in the graph of FIG. 8 is represented by the following mathematical formula.

Y=3.8*X−2.994

According to the finding by the inventor of the present invention, the golf ball 2 whose coordinate (X,Y) is on or below the straight line L3 has particularly excellent flight performance. In other words, the golf ball 2 that meets the following mathematical formula (III) has excellent flight performance. The reason is inferred to be that turbulization is prompted.

Y≦3.8*X−2.994   (III)

When arranging the dimples 10, in many cases, a designer initially designs an arrangement of basic dimples 10 and then arranges small dimples 10 in narrow zones each surrounded by a plurality of the dimples 10, in order to further increase an occupation ratio. However, the small dimples 10 contribute to the effect of increasing the occupation ratio but impair the effect of decreasing the standard deviation. The arrangement of the small dimples 10 does not correspond to the purport of the present invention. In designing a dimple pattern according to the present embodiment, the designer focuses on the center-to-center distance between adjacent dimples 10 from the stage of designing the basic dimples 10. The designer designs the pattern with due consideration to making the center-to-center distance between the adjacent dimples 10 as small as possible. Therefore, even when no small dimple 10 is arranged, the occupation ratio can be increased.

FIG. 9 shows a cross section along a plane passing through the center of the dimple 10 and the center of the golf ball 2. In FIG. 9, the top-to-bottom direction is the depth direction of the dimple 10. In FIG. 9, what is indicated by a chain double-dashed line 14 is the phantom sphere. The surface of the phantom sphere is the surface of the golf ball 2 when it is postulated that no dimple 10 exists. The dimple 10 is recessed from the surface of the phantom sphere. The land 12 coincides with the surface of the phantom sphere. In the present embodiment, the cross-sectional shape of each dimple 10 is substantially a circular arc.

In FIG. 9, what is indicated by a double ended arrow Dm is the diameter of the dimple 10. The diameter Dm is the distance between two tangent points Ed appearing on a tangent line Tg that is drawn tangent to the far opposite ends of the dimple 10. Each tangent point Ed is also the edge of the dimple 10. The edge Ed defines the contour of the dimple 10. In FIG. 9, what is indicated by a double ended arrow Dp is the depth of the dimple 10. The depth Dp is the distance between the deepest part of the dimple 10 and the tangent line Tg.

The diameter Dm of each dimple 10 is preferably equal to or greater than 2.0 mm but equal to or less than 6.0 mm. The dimple 10 having a diameter Dm of 2.0 mm or greater contributes to turbulization. In this respect, the diameter Dm is more preferably equal to or greater than 2.2 mm and particularly preferably equal to or greater than 2.4 mm. The dimple 10 having a diameter Dm of 6.0 mm or less does not impair a fundamental feature of the golf ball 2 being substantially a sphere. In this respect, the diameter Dm is more preferably equal to or less than 5.8 mm and particularly preferably equal to or less than 5.6 mm.

In FIG. 9, what is indicated by an arrow CR is the curvature radius of the dimple 10. The curvature radius CR is calculated by the following mathematical formula (1)

CR=(Dp ² +Dm ²/4)/(2*Dp)   (1)

Also in the case of a dimple 10 whose cross-sectional shape is not a circular arc, the curvature radius CR is approximately calculated on the basis of the above mathematical formula (1).

From the standpoint that a sufficient occupation ratio X is obtained, the total number N of the dimples 10 is preferably equal to or greater than 300, more preferably equal to or greater than 310, and particularly preferably equal to or greater than 320. From the standpoint that each dimple 10 can contribute to turbulization, the total number N is preferably equal to or less than 400, more preferably equal to or less than 390, and particularly preferably equal to or less than 380.

In the present invention, the “volume of the dimple 10” means the volume of the portion surrounded by the surface of the dimple 10 and the plane including the contour of the dimple 10. In light of suppression of rising of the golf ball 2 during flight, the total volume of all the dimples 10 is preferably equal to or greater than 250 mm³, more preferably equal to or greater than 260 mm³, and particularly preferably equal to or greater than 270 mm³. In light of suppression of dropping of the golf ball 2 during flight, the total volume is preferably equal to or less than 400 mm³, more preferably equal to or less than 390 mm³, and particularly preferably equal to or less than 380 mm³.

In light of suppression of rising of the golf ball 2 during flight, the depth Dp of each dimple 10 is preferably equal to or greater than 0.05 mm, more preferably equal to or greater than 0.08 mm, and particularly preferably equal to or greater than 0.10 mm. In light of suppression of dropping of the golf ball 2 during flight, the depth Dp is preferably equal to or less than 0.60 mm, more preferably equal to or less than 0.45 mm, and particularly preferably equal to or less than 0.40 mm.

EXAMPLES Example 1

A rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), 35 parts by weight of zinc diacrylate, 5 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.5 parts by weight of diphenyl disulfide, and 0.9 parts by weight of dicumyl peroxide. This rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 170° C. for 18 minutes to obtain a core with a diameter of 39.7 mm. The amount of barium sulfate was adjusted such that the weight of a golf ball is 45.6 g.

A resin composition was obtained by kneading 50 parts by weight of an ionomer resin (trade name “Surlyn 8945”, manufactured by E.I. du Pont de Nemours and Company), 50 parts by weight of another ionomer resin (“Himilan AM7329”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), 4 parts by weight of titanium dioxide, and 0.04 parts by weight of ultramarine blue with a twin-screw kneading extruder. The core was covered with the resin composition by injection molding to form a mid layer with a thickness of 1.0 mm.

A paint composition (trade name “POLIN 750LE”, manufactured by SHINTO PAINT CO., LTD.) including a two-component curing type epoxy resin as a base polymer was prepared. The base material liquid of this paint composition includes 30 parts by weight of a bisphenol A type solid epoxy resin and 70 parts by weight of a solvent. The curing agent liquid of this paint composition includes 40 parts by weight of a modified polyamide amine, 55 parts by weight of a solvent, and 5 parts by weight of titanium oxide. The weight ratio of the base material liquid to the curing agent liquid is 1/1. This paint composition was applied to the surface of the mid layer with a spray gun, and kept at 23° C. for 6 hours to obtain a reinforcing layer with a thickness of 10 μm.

A resin composition was obtained by kneading 100 parts by weight of a thermoplastic polyurethane elastomer (trade name “Elastollan XNY85A”, manufactured by BASF Japan Ltd.) and 4 parts by weight of titanium dioxide with a twin-screw kneading extruder. Half shells were formed from this resin composition by compression molding. The sphere consisting of the core, the mid layer, and the reinforcing layer was covered with two of these half shells. The sphere and the half shells were placed into a final mold that includes upper and lower mold halves each having a hemispherical cavity and having a large number of pimples on its cavity face, and a cover was obtained by compression molding. The thickness of the cover was 0.5 mm. A large number of dimples having a shape that is the inverted shape of the pimples were formed on the cover. A clear paint including a two-component curing type polyurethane as a base material was applied to this cover to obtain a golf ball of Example 1 with a diameter of about 42.7 mm and a weight of about 45.6 g. The specifications of the dimples of the golf ball are shown in Table 1 below.

Examples 2 to 7 and Comparative Examples 1 to 5

Golf balls of Examples 2 to 7 and Comparative Examples 1 to 5 were obtained in the same method as Example 1, except the specifications of the dimples were as shown in Tables 1 to 3 below. The golf ball according to Comparative Example 1 has the same dimple pattern as that of the golf ball according to Example 1 described in JP2009-95593. The golf ball according to Comparative Example 2 has the same dimple pattern as that of the golf ball according to Comparative Example 2 described in JP2008-389. The golf ball according to Comparative Example 3 has the same dimple pattern as that of the golf ball according to Comparative Example 2 described in JP2011-30909.

TABLE 1 Specifications of Dimples Curvature Number Diameter Depth radius of Dm Dp CR Volume Type dimples (mm) (mm) (mm) (mm³) Example A 16 4.600 0.135 19.66 1.123 1 B 30 4.500 0.135 18.82 1.075 C 30 4.400 0.135 17.99 1.028 D 150 4.300 0.135 17.19 0.982 E 30 4.200 0.135 16.40 0.936 F 66 4.100 0.135 15.63 0.892 G 10 3.800 0.135 13.44 0.767 H 12 3.400 0.135 10.77 0.614 Example A 28 4.500 0.135 18.82 1.075 2 B 122 4.400 0.135 17.99 1.028 C 100 4.300 0.135 17.19 0.982 D 74 4.150 0.135 16.01 0.914 Example A 252 4.300 0.135 17.19 0.982 3 B 70 4.100 0.135 15.63 0.892 C 2 3.600 0.135 12.07 0.688 Example A 132 4.720 0.135 20.70 1.182 4 B 18 4.520 0.135 18.98 1.084 C 28 4.420 0.135 18.16 1.037 D 54 4.320 0.135 17.35 0.991 E 68 4.120 0.135 15.78 0.901 F 6 3.620 0.135 12.20 0.696 G 16 3.320 0.135 10.27 0.586

TABLE 2 Specifications of Dimples Curvature Number Diameter Depth radius of Dm Dp CR Volume Type dimples (mm) (mm) (mm) (mm³) Example A 8 4.800 0.135 21.40 1.223 5 B 18 4.600 0.135 19.66 1.123 C 32 4.500 0.135 18.82 1.075 D 34 4.400 0.135 17.99 1.028 E 166 4.300 0.135 17.19 0.982 F 18 4.200 0.135 16.40 0.936 G 46 4.100 0.135 15.63 0.892 H 22 3.200 0.135 9.55 0.544 Example A 252 4.300 0.135 17.19 0.982 6 B 70 4.050 0.135 15.26 0.871 C 2 3.200 0.135 9.55 0.544 Example A 172 4.300 0.135 17.19 0.982 7 B 150 4.210 0.135 16.48 0.941 C 2 3.800 0.135 13.44 0.767

TABLE 3 Specifications of Dimples Curvature Number Diameter Depth radius of Dm Dp CR Volume Type dimples (mm) (mm) (mm) (mm³) Compa. A 26 4.500 0.142 17.90 1.131 Example B 88 4.400 0.142 17.11 1.081 1 C 102 4.300 0.142 16.35 1.033 D 94 4.100 0.142 14.87 0.939 E 14 3.600 0.142 11.48 0.724 Compa. A 60 4.100 0.145 14.56 0.959 Example B 84 4.000 0.144 13.96 0.906 2 C 216 3.900 0.141 13.55 0.844 Compa. A 40 4.650 0.146 18.59 1.241 Example B 70 4.550 0.146 17.80 1.189 3 C 40 4.450 0.146 17.03 1.137 D 110 4.300 0.146 15.90 1.062 E 20 4.150 0.146 14.82 0.989 F 40 3.900 0.146 13.10 0.874 G 12 2.850 0.146 7.03 0.467 Compa. A 108 4.500 0.135 18.82 1.075 Example B 78 4.400 0.135 17.99 1.028 4 C 20 4.300 0.135 17.19 0.982 D 100 4.100 0.135 15.63 0.892 E 18 3.600 0.135 12.07 0.688 Compa. A 92 4.700 0.135 20.52 1.172 Example B 28 4.500 0.135 18.82 1.075 5 C 42 4.400 0.135 17.99 1.028 D 34 4.300 0.135 17.19 0.982 E 98 4.100 0.135 15.63 0.892 F 28 3.630 0.135 12.27 0.700 G 10 3.100 0.135 8.97 0.511

[Flight Distance Test]

A driver with a head made of a titanium alloy (trade name “SRIXON Z-TX”, manufactured by DUNLOP DPORTS CO. LTD., shaft hardness: X, loft angle:)8.5° was attached to a swing machine manufactured by Golf Laboratories, Inc. A golf ball was hit under the conditions of: a head speed of 50 m/sec; a launch angle of about 10°; and a backspin rate of about 2500 rpm, and the distance from the launch point to the stop point was measured. At the test, the weather was almost windless. The average value of data obtained by 20 measurements is shown in Tables 4 to 6 below.

TABLE 4 Results of Evaluation Example Example Example Example 1 2 3 4 Plan view FIG. 10 FIG. 2 FIG. 16 FIG. 22 Bottom view FIG. 11 FIG. 3 FIG. 17 FIG. 23 Right side view FIG. 12 FIG. 4 FIG. 18 FIG. 24 Front view FIG. 13 FIG. 5 FIG. 19 FIG. 25 Left side view FIG. 14 FIG. 6 FIG. 20 FIG. 26 Back view FIG. 15 FIG. 7 FIG. 21 FIG. 27 Number N of 344 324 324 322 dimples Occupation 0.853 0.830 0.804 0.860 ratio X Standard 0.223 0.109 0.097 0.360 deviation Y (mm) Mathematical Met Met Met Met formula (I) Mathematical Met Met Met Unmet formula (II) Mathematical Met Met Unmet Unmet formula (III) Flight distance 260.6 259.8 258.2 257.0 (m)

TABLE 5 Results of Evaluation Example Example Example 5 6 7 Plan view FIG. 28 FIG. 34 FIG. 40 Bottom view FIG. 29 FIG. 35 FIG. 41 Right side view FIG. 30 FIG. 36 FIG. 42 Front view FIG. 31 FIG. 37 FIG. 43 Left side view FIG. 32 FIG. 38 FIG. 44 Back view FIG. 33 FIG. 39 FIG. 45 Number N of 344 324 324 dimples Occupation 0.858 0.799 0.805 ratio X Standard 0.310 0.131 0.057 deviation Y (mm) Mathematical Met Met Met formula (I) Mathematical Met Unmet Met formula (II) Mathematical Unmet Unmet Met formula (III) Flight distance 258.6 257.1 259.4 (m)

TABLE 6 Results of Evaluation Compa. Compa. Compa. Compa. Compa. Example Example Example Example Example 1 2 3 4 5 Number N of 324 360 332 324 332 dimples Occupation 0.806 0.773 0.849 0.820 0.844 ratio X Standard 0.192 0.076 0.357 0.235 0.377 deviation Y (mm) Mathematical Unmet Unmet Unmet Unmet Unmet formula (I) Mathematical Unmet Unmet Unmet Unmet Unmet formula (II) Mathematical Unmet Unmet Unmet Unmet Unmet formula (III) Flight distance 255.4 251.9 252.3 254.7 255.0 (m)

As shown in Tables 4 to 6, the golf ball of each Example has excellent flight performance. From the results of evaluation, advantages of the present invention are clear.

The aforementioned dimples are applicable to a one-piece golf ball, a two-piece golf ball, a four-piece golf ball, a five-piece golf ball, a six-piece golf ball, a thread-wound golf ball, and the like in addition to a three-piece golf ball. The above descriptions are merely for illustrative examples, and various modifications can be made without departing from the principles of the present invention. 

What is claimed is:
 1. A golf ball having a large number of dimples on a surface thereof, the golf ball meeting the following mathematical formula (I): Y≦3.8*X−2.894   (I), where X represents a ratio of a sum of areas of all the dimples to a surface area of a phantom sphere of the golf ball, and Y represents a standard deviation (mm) of diameters of all the dimples.
 2. The golf ball according to claim 1, wherein the ratio X is equal to or greater than 0.78.
 3. The golf ball according to claim 1, wherein the ratio X is equal to or less than 0.95.
 4. The golf ball according to claim 1, wherein the standard deviation Y is equal to or less than 0.30 mm.
 5. The golf ball according to claim 1, wherein a number of the dimples is equal to or greater than 300 but equal to or less than
 400. 6. The golf ball according to claim 1, wherein a contour of each dimple is circular.
 7. The golf ball according to claim 6, wherein a diameter of each dimple is equal to or greater than 2.0 mm but equal to or less than 6.0 mm.
 8. The golf ball according to claim 1, wherein a depth of each dimple is equal to or greater than 0.05 mm but equal to or less than 0.60 mm.
 9. The golf ball according to claim 1, wherein a total volume of the dimples is equal to or greater than 250 mm³ but equal to or less than 400 mm³.
 10. The golf ball according to claim 1, wherein the golf ball meets the following mathematical formula (II): Y≦3.8*X−2.944   (II).
 11. The golf ball according to claim 10, wherein the golf ball meets the following mathematical formula (III): Y≦3.8*X−2.994   (III). 